Recently, in a vehicle, a tire pressure monitoring system (TPMS) which detects an air-pressure drop of a tire installed in the vehicle to notify the detected air-pressure drop to a driver has been installed.
When the air pressure of the tire is decreased, the vehicle easily slides and thus a major accident may be caused, a fuel consumption amount is increased, and thus, fuel efficiency deteriorates. Further, when the air pressure of the tire is decreased, a lifespan of the tire is decreased and riding quality and braking power are largely decreased.
The TPMS notifies the pressure drop of the tire to the driver by checking a pressure state of the tire to prevent the problems from being generated.
The TPMS may be largely divided into a direct type and an indirect type.
The direct type is to directly measure air pressure of the tire by installing a pressure sensor inside a tire wheel. The direct type may detect the reduction of the air pressure of the tire with high accuracy, but has disadvantages in terms of a technique and cost in that a dedicated wheel is required and there is a problem in performance in an actual environment.
The indirect type is a method for estimating tire air pressure from rotation information of the tire. The indirect type TPMS may be particularly classified into a dynamic loaded radius (DLR) analysis type and a resonance frequency method (RFM) analysis type again. The types are briefly abbreviated as the radius analysis and the frequency analysis.
The frequency analysis type is a type of detecting a difference between a decompressed tire and a normal pressure tire by using a change in frequency characteristic of a rotation speed signal of the wheel. In the frequency analysis type, when the corresponding resonance frequency is calculated to be relatively lower than a reference frequency estimated during initialization by paying attention to the resonance frequency which may be calculated by frequency analysis of the wheel rotation speed signal, it is determined that the tire is decompressed.
The radius analysis type is a type for detecting pressure drop by comparing rotation speeds of four tires by using a phenomenon in which the decompressed tire has a small dynamic loaded radius while driving and as a result, rotates faster than the normal tire.
Meanwhile, the vehicle mass is very important information in various chassis control systems. For example, in various chassis control systems, a tire pressure monitoring system (TPMS), an electronic stability controller (ESC), active roll stabilization (ARS) device, a continuous damping controller (CDC), and the like may be included. When variation of the mass of the vehicle occurs, a slip of the tire occurs and thus, an engine RPM may vary. Further, in the period, a transmission shock is generated and thus, riding quality may be decreased.
The vehicle mass is modeled by a spring, a damper, and a vehicle weight to be estimated by applying an equation of motion of moving and vibrating by external force and internal driving force to the vehicle.
As another method, in a method for measuring vehicle body mass to be installed in the vehicle, an expensive garage sensor is additionally installed in the vehicle to estimate the mass of the vehicle.
However, in the method for measuring the vehicle mass, the vehicle mass is not accurately estimated. Further, a garage sensor for measuring the vehicle mass needs to be additionally installed, and inaccurate estimation of the vehicle mass influences control performance.